It is well known in the art to equip vacuum cleaners with filter bags for filtering dust and dirt particles out of a particle laden air stream created by a vacuum cleaner blower. These filter bags may comprise a single bag element or multiple bag elements of a porous paper or fiber material defining a matrix which traps particulate matter suspended in the air stream while allowing clean air to pass through each bag element and into the environment. Such filter bags are generally disposable and may be detached from a vacuum cleaner and discarded when they have become full of dirt or the openings therethrough have become clogged with dirt.
The efficiency of a vacuum cleaner is affected, in part, by the resistance to air flow imposed by the vacuum cleaner filter bag attached thereto. The more porous the bag elements of the filter bag, the less effort is needed to force air through the filter bag to filter particulate matter from the air. However, if a bag element is too porous, much of the dirt and dust picked up by the vacuum cleaner will pass through the bag element or elements and return to the environment, thus reducing the utility and efficiency of the vacuum cleaner. If bag elements with a tight fiber matrix are used, however, a great amount of force will be needed by the vacuum motor to force air therethrough. Thus, when very tightly woven bag elements are used, the vacuum cleaner must have a fairly powerful motor. Even when a powerful motor is used, its efficiency is decreased by the resistance to air flow imposed by the bag elements of the filter bag. Also, when bag elements having very small openings are employed, these openings quickly become clogged with dirt, decreasing the efficiency of the vacuum and straining the vacuum cleaner motor. Such a filter bag must be replaced frequently adding to the operating cost of the vacuum cleaner. An acceptable balance must therefore be reached between the size of the motor used, the frequency with which the filter bag must be changed, and the percentage of dust and dirt which will be removed from the air by the bag elements. Most attempts to improve vacuum cleaner filter bag design in one of these three areas result in a worsening of the other problems. Thus a filter bag having bag elements with a very fine matrix for use in settings where removing substantially all dust from the discharge is imperative generally must be changed frequently and be used with a vacuum cleaner having a relatively large motor. When a small motor is to be used for reasons of economy, only a lesser degree of dirt removal can be obtained. No known filter bag design adequately addresses all of these problems simultaneously.